In Dec 2015, Microsoft released an update (KB3114409) which causes Outlook 2010 to start only in Safe Mode. This might not be recognized at first sight, because no dialog box appears like there was a damaged add-in etc. But you might see the mail content preview area is not loaded and the header bar shows a text “Safe Mode”.
Usually, at the next start after Safe Mode, Outlook should start in Normal Mode, which it does not if update KB3114409 is installed. Another weird fact is that this update was published for local WSUS servers, and update KB3114560 (which solves this issue) is not (at least not at this date).
You can download the fix from here, but it is not possible to import it into WSUS. You could run it e.g. via GPO -> Startup scripts.
One alternative would be to disable Safe Mode, but it is not recommended. Read the tutorial here.
Another alternative method would be to reject the original update KB3114409 in WSUS. To uninstall it from all clients, use “Approve -> Approved for Removal”.
Clients keep getting prompted to uninstall this update after “approval for removal” via WSUS. So once your desktops are all unpatched, you will have to decline the update.
A new Revision of update KB3114409 is available via WSUS, the issue seems to be solved now.